Metal frames have long been used as the structural support for a variety of seating and furniture applications. Such frames are used to anchor some type of fabric, rubber webbing, or other covering material in order to create a support surface to which or upon which other parts of a seat may be attached or otherwise constructed. For instance, foam padding, cushions, and the like are routinely incorporated onto such a support structure.
The method of attaching the support surface material to the furniture frame has been achieved in a variety of ways. Conventionally, the support surface has been attached to the frame using means which are either integrated into the fabric structure or which are external. Such methods include sewn loops or sleeves, tab constructions, laces or other ties, hook and loop attachments (e.g., Velcro.TM.), snaps, zippers, staples, nails, and the like.
U.S. Pat. No. 4,230,365 to Messinger discloses a fabric-covered furniture support frame, in which a fabric sleeve is drawn over a peripheral furniture frame. The fabric sleeve is comprised of a two-way stretch knitted material or a non-stretch, woven material, and the sleeve may be impregnated with a resinous material to add stiffness. The peripheral frame features two side rail members and a plurality of braces connecting the rail members. Unlike the fabric sleeve of Messinger, the fabric hoop utilized in the present invention fits snugly around the furniture frame, with no ends remaining that require additional manipulation. The present invention further provides an automated means for attaching a stretchable fabric to a furniture frame, in the form of a useful and economical device.
Hoops, or cylindrical sleeves, of elastomeric fabrics have also been used and are conventionally applied by stretching the entire fabric hoop with a mechanical means and then inserting the furniture frame into the open, outstretched hoop. The stretching tension on the hoop is then removed and the hoop is allowed to reduce its size until, in its partially relaxed state, it is tight on the frame. Such a process is traditionally used for hoops made from rubber webbing because this type of webbing can be significantly over-stretched, up to about 300% (i.e., about three times) of its normal, relaxed circumference. The stretch of the webbing when attached to the frame is about 200% (i.e., about twice) of its normal circumference. Such stretch is acceptable in rubber webbing, but is very difficult to achieve with polyester elastomeric fabrics because of the relatively limited stretch characteristics of these fabrics.
For purposes of discussion herein, it is helpful to define the following terms. "Elastomeric fabrics" are fabrics made of woven or knitted yarns of various synthetic polymers; such yarns, and the fabrics constructed from such yarns, exhibit some properties that are similar to those of natural rubber, such as high stretchability and recovery. "Elastomeric recovery" is the degree to which an elastomeric fabric returns to its original size and shape after being placed under tension and deformed. The term "hoop" refers to a cylindrical sleeve or loop of fabric, which may be created by, for example, joining the opposite ends of a rectangular piece of elastomeric fabric in a manner that will maintain the integrity of the loop when the loop is placed under tension. Such methods include stitching, bonding, or other suitable seaming means. Alternatively, the hoop may be in the form of fabric that has been formed as a continuous loop of fabric, with no need for seaming or joining.
When referring to the stretch exhibited by the fabric hoops, several terms will be used as defined herein. The term "relaxed" refers to a fabric in an unstretched condition (that is, having no applied tension). The term "over-stretch" refers to the stretch exerted on the fabric as it is being applied to the furniture frame. The term "prestretch" refers to the degree of stretch of a fabric once the fabric hoop is positioned on the furniture frame. The term "load stretch" refers to the degree of stretch experienced by the fabric as it bears a weight in the course of functioning as a seating device, such as that exerted by a seat occupant. The term "total stretch" refers to the sum of the prestretch and the load stretch. The "maximum stretch" of a polyester elastomeric fabric is the stretch beyond which the fabric loses its elastomeric recovery, which, for elastomeric fabrics made of the preferred polyester material, is generally being in the range of 25% to 30% of the original, untensioned dimension of the fabric. The total stretch of the fabric should not exceed the maximum stretch of the fabric.
Because polyester elastomeric fabrics are capable of achieving a maximum stretch of only about 25% or 30% of their original, untensioned dimension (which dimension shall be referred to as length, as in circumferential length), certain adjustments must be made in stretching these fabrics for attachment to a furniture frame. If the fabric is stretched beyond the maximum stretch, then it is likely to lose its elastomeric recovery. In seating applications, loss of elastomeric recovery adversely affects the comfort of the seat occupants and the durability of the seat during repeated use.
A problem encountered in the manufacture of seating using rubber webbing is that the majority of rubber webbing tends to stick to the frame during application, making such webs relatively difficult to position or re-position on the frame. On the other hand, the polyester elastomeric fabrics utilized in the present invention do not have the same tendency as the rubber web to stick to the frame. Rather, these fabrics, when used in hoops that are in a stretched configuration, tend to slide easily onto the frame and into position, requiring a lower degree of over-stretch than their rubber counterparts and making them more easily utilized in this type of application. When properly positioned and relaxed, hoops of these materials provide a firm and relatively immobile grip, and remain fixed in position on the frame during use, yet may be readily adjusted or removed as required. Thus, the present invention is able to accommodate the characteristic of polyester's limited stretch (as compared with rubber) and, at the same time, utilize, to commercial advantage, the relatively low sliding friction between the tensioned fabric and the metal frame.
In addition to the ease of use during manufacturing (e.g., from relatively low sliding friction between the fabric and the frame), several other advantages are realized by using polyester elastomers instead of rubber webbing. It has been found that, over time, the polyester elastomeric fabric does not tend to deteriorate as quickly as the rubber webbing. Furthermore, the elastomeric fabrics are suitable for applications in which such fabrics can act as both the support surface and the face fabric (i.e., with no additional surface fabric being attached). Another significant consideration, in this regard, is the increased comfort of the occupant when seated in a chair whose support surface is made from elastomeric fabrics as compared to the chair whose support surface is made from rubber webbing that, in turn, is covered with padding, face fabrics, or the like. This added comfort is believed to be due to the superior ability of such fabrics to distribute weight and to allow for the circulation of air around and through the support surface. Thus, durability, comfort, and the possible elimination of face fabrics are advantages over the seating support surfaces of the prior art.
The device disclosed herein is capable of realizing the above-described benefits. In particular, the device disclosed herein is capable of achieving, in polyester elastomeric fabric, a desired level of stretch and is capable of attaching such fabric to a metal furniture frame by tension alone, with no other attachment means being required. For these reasons, the present invention represents a useful advancement over the prior art.